I don't know if there's any performance penalty running two pairs of memory sticks of different sizes. If not, I'm going to add two 8GB sticks for a total of 24GB. I usually order from OWC, but they're not listing the 1600MHz memory that the 2012 iMac uses yet, but I'm hoping that it's not much more expensive than the 1333MHz memory.

Just ordered from Crucial. I used ebates which has 6% cashback and a 5% off coupon, also used their 16GB kit that isn't the one they bring up when you select the iMac but it's the exact same specs (CT2KIT102464BF160B). So that kit with the coupon is $72.19 and you'll get 6% back in cashback if you use ebates. I know there was a better deal for G.Skill but I like Crucial better. Plan on adding the kit to have a total of 24GB.

those of you pulling the original 8 should consider selling it cheap to someone here. with paypal or a similar service, you could make a safe transaction and not bother with the additional fees of ebay. The benefit over somewhere like Craigslist, your working with a fellow iMac owner

No math seems to be hard for you: there are no 6 nor 12 nor 3 GB sticks out there. How could you put a 6 GB stick into one slot?

He's talking about an 8gig and a 4 gig in one channel to make up the 12 he's referring to. My question is that the way you should do it. Or have same memory sizes to match the one going into the same channel.

no math seems to be hard for you: There are no 6 nor 12 nor 3 gb sticks out there. How could you put a 6 gb stick into one slot?

-.-"

8 + 4 + 8 + 4 = 24.

Quote:

Originally Posted by Hesays

I'm honestly unsure on how this works. So is it better to have 8 and 4 in one channel and 8 and 4 in the other. Or 8 and 8 and 4 and 4 beside each other. Thoughts memory Gurus?

8 + 4 in each channel will give you dual channel. 8 + 8 in one and 4 + 4 in another will give you async dual channel which is a very small performance loss. Honestly it doesn't matter but if you want to be 100% sure you don't lose out on any performance just put 8 + 4 in each channel. I don't know the DIMM assignments for the new iMac but it is not hard to figure out once you get it (you have 50% chance of getting it right lol).

He's talking about an 8gig and a 4 gig in one channel to make up the 12 he's referring to. My question is that the way you should do it. Or have same memory sizes to match the one going into the same channel.

I would simply check with Apple on proper instillation. Might even be in the manual. it can't be that hard to figure out, as they will have installed the 2x4GB into slots to take advantage of the performance channels, leaving the two remaining for whatever you want to add.

8 + 4 in each channel will give you dual channel. 8 + 8 in one and 4 + 4 in another will give you async dual channel which is a very small performance loss. Honestly it doesn't matter but if you want to be 100% sure you don't lose out on any performance just put 8 + 4 in each channel. I don't know the DIMM assignments for the new iMac but it is not hard to figure out once you get it (you have 50% chance of getting it right lol).

For the record, unless someone on here wants to sell me their spare 4GBx2 at a reasonable price, I will eventually buy a pair of 8GBs to jump to 24. However, as I get so few PageOuts on my three year old MacBook that I bumped to 8GB (exceeding Apple's Max of 6GB), I can afford to wait a few months.

Either way, may just jump on Apple's site and use the Chat to ask for an official upgrade answer...

probably less than 50%, as you have 4 DIMMs and 4 slots, with 2 types of DIMMs, but as I only got 4 hours of sleep waiting up to order my iMac, I'm not doing the probability in my head right now

It will certainly be less than 50% just trying randomly. But in reality it will be either 8/4/8/4 or 8/8/4/4.

Quote:

Originally Posted by Foxer

I came to ask this precise question. The consensus seems to be that, if you buy a 16GB kit (8x2) and put a stick in each empty slot, you'll be in sync and problem free. Right?

Short answer is yes. You bring up a good point though. Apple undoubtedly installed the existing RAM in dual channel so if you buy a 16GB kit you are guaranteed to get dual channel unless you bought the wrong RAM.